1. Field of the Invention
The invention relates to a defect inspection method for a magnetic recording medium used in a hard disk apparatus or a floppy disk apparatus and a defect inspection method for a master information carrier used for magnetically transferring an information signal to a magnetic recording medium. The invention also relates to a magnetic film pattern magnetic transfer method by use of a master information carrier, and more particularly to a magnetic recording/reproduction apparatus.
2. Description of the Related Art
A magnetic recording medium mounted to a magnetic recording/reproduction apparatus such as a hard disk drive apparatus records thereon an information signal used for a servo mechanism for a recording/reproduction head. This information signal may be a tracking servo signal, an address information signal, a reproduction clock signal or the like. With a recent increase in the track density, the capacity of information signals that can be recorded by a servo writer may not be increased any more. To solve this problem, there is suggested such a system that a so-called master information carrier is prepared to thereby transfer and record an information signal thereon to a magnetic recording medium. The master information carrier is formed of a magnetic portion made of a ferromagnetic material on a non-magnetic base surface in such a pattern shape as to correspond to an information signal. The master information carrier is brought in contact with the surface of the magnetic recording medium on which a ferromagnetic thin film or a ferromagnetic powder-applied layer is formed and then has an external magnetic field applied thereon, to thereby transfer and record to the magnetic recording medium a magnetized pattern having such a pattern shape as to correspond to the information signal on the master information carrier.
In this case, it is necessary to record the information signal to the magnetic recording medium uniformly and in a stable manner. If the master information carrier has an abnormal protrusion or foreign matter on its surface, however, a pit may occur in the surface of the magnetic recording medium when it comes in close contact with the master information carrier.
FIGS. 31A and 31B show a surface a of the magnetic recording medium after magnetic transfer by use of a master information carrier which has an abnormal protrusion or foreign matter. A reference symbol b indicates a pit and a reference symbol c indicates a minute protrusion generated in reaction to the formation of the pit. FIG. 31A shows a picture, while FIG. 31B shows implicitly the position and the size of the surface a, the pit b, and the minute protrusion c in correspondence with the unclear picture. FIG. 32 shows a cross section of the pit as measured. As shown in FIG. 32, surrounding the pit b indented by approximately 50 nm from the surface of the magnetic recording medium is present a minute protrusion c with a height of approximately 20 nm. Typically, a float amount of the head slider with respect to the surface of the magnetic recording medium is approximately 20 nm. If there is a minute protrusion of approximately 20 nm on the magnetic recording medium, therefore, the magnetic head may possibly come in contact with the magnetic recording medium. Immediately after they com in contact with each other, the magnetic head is hit and has a larger clearance with respect to the magnetic recording medium, thus deteriorating the recording/reproduction performance of the signal. In addition, if the magnetic head physically comes in contact with the magnetic recording medium, the magnetic head may suffer from a shortened service life and the magnetic recording medium may be damaged.
FIG. 33 shows a result of optical measurement of a state of a protrusion on the surface of a magnetic recording medium after magnetic transfer in a case where there is an abnormal protrusion or foreign matter on the surface of a master information carrier during the magnetic transfer. It shows the presence of the protrusion as large as a 20 nm or more. The protrusion affects the recording/reproduction performance and the service life of the magnetic head the more as the float amount of the magnetic head becomes smaller due to an increasing recording density. To guard against this, it is necessary to inspect a defect on the surface of the master information carrier. It is, however, difficult to inspect an abnormal protrusion or foreign matter present on the master information carrier because of the presence of a pattern shape corresponding to the information signal. In optical inspection of a surface defect of the magnetic recording medium after magnetic transfer, the surface of the magnetic recording medium must be very smooth in order to identify a minute defect caused by magnetic transfer, thus increasing the costs. A minute defect, if any on the magnetic recording medium before magnetic transfer, is difficult to discriminate from a defect caused by magnetic transfer. Minute foreign matter, if any, on the surface of the master information carrier, always generates a defect on the magnetic recording medium. The defect, therefore, constitutes a major problem even if it is minute.
Even if there is no abnormal protrusion or foreign matter on the master information carrier or the magnetic recording medium, external foreign matter may be caught between the master information carrier and the magnetic recording medium when magnetic transfer is performed. Waste dust from the magnetic transferring apparatus may cause a defect in some cases. In such a case, foreign matter remains on or a pit is generated in the surface of the magnetic recording medium after magnetic transfer.